AMDGPU: Remove SIFixSGPRLiveRanges pass

Summary:
This pass is unnecessary and overly conservative. It was motivated by
situations like

  def %vreg0:SGPR_32
  ...
if-block:
  ..
  def %vreg1:SGPR_32
  ...
else-block:
  ...
  use %vreg0:SGPR_32
  ...

and similar situations with uses after the non-uniform control flow, where
we are not allowed to assign %vreg0 and %vreg1 to the same physical register,
even though in the original, thread/workitem-based CFG, it looks like the
live ranges of these registers do not overlap.

However, by the time register allocation runs, we have moved to a wave-based
CFG that accurately represents the fact that the wave may run through both
the if- and the else-block. So the live ranges of %vreg0 and %vreg1 already
overlap even without the SIFixSGPRLiveRanges pass.

In addition to proving this change correct, I have tested it with Piglit
and a small number of other tests.

Reviewers: arsenm, tstellarAMD

Subscribers: MatzeB, arsenm, llvm-commits

Differential Revision: http://reviews.llvm.org/D19041

llvm-svn: 266345

1 files changed, 0 insertions, 7 deletions

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp b/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
index dce2a92..29faf83 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
@@ -48,7 +48,6 @@ extern "C" void LLVMInitializeAMDGPUTarget() {
   initializeSILowerI1CopiesPass(*PR);
   initializeSIFixSGPRCopiesPass(*PR);
   initializeSIFoldOperandsPass(*PR);
-  initializeSIFixSGPRLiveRangesPass(*PR);
   initializeSIFixControlFlowLiveIntervalsPass(*PR);
   initializeSILoadStoreOptimizerPass(*PR);
   initializeAMDGPUAnnotateKernelFeaturesPass(*PR);
@@ -351,16 +350,10 @@ void GCNPassConfig::addPreRegAlloc() {
 }
 
 void GCNPassConfig::addFastRegAlloc(FunctionPass *RegAllocPass) {
-  addPass(&SIFixSGPRLiveRangesID);
   TargetPassConfig::addFastRegAlloc(RegAllocPass);
 }
 
 void GCNPassConfig::addOptimizedRegAlloc(FunctionPass *RegAllocPass) {
-  // We want to run this after LiveVariables is computed to avoid computing them
-  // twice.
-  // FIXME: We shouldn't disable the verifier here. r249087 introduced a failure
-  // that needs to be fixed.
-  insertPass(&LiveVariablesID, &SIFixSGPRLiveRangesID, /*VerifyAfter=*/false);
   TargetPassConfig::addOptimizedRegAlloc(RegAllocPass);
 }